Infrared analyzers generally feature irradiating a food or organic sample with light in the near-infrared portion of the spectrum. The underlying principle of the analyzer is to photometrically measure the spectral variations in the reflected light, which variations are due to the spectrally selective absorption of the light by organic constituents in the sample. Light measurements conducted at several different wavelengths in the near infrared range will provide information determinative of the relative concentrations of the sample constituents as a result of their selectivity at the various wavelengths of light. A system of this general type is described in U.S. Pat. No. 3,776,642, issued to Anson et al. on Dec. 4, 1973.
The sample is usually measured concurrently with a reference to establish a proper measurement level and remove interferences peculiar to the system. Sample and reference measurements are often concurrently measured by means of a dual beam system, i.e., one beam directed at the sample and another beam directed at the reference. The necessity for measuring the sample and reference at the same time is to avoid or minimize errors due to drift in the measuring system.
Drift between sample and reference measurements cannot be tolerated due to the extreme accuracies demanded from this type of analyzer. Therefore, extreme care must be exercised to prevent a drift condition.
In some devices, a single beam is used to measure the sample and the reference. Drift between sample and reference measurements is eliminated in these systems by very rapidly switching the light beam between sample and reference. However, such systems require very complex and costly optics to provide this rapid light beam switching.
The present invention is for a single-beam system which is sensitive, less complex and of lower cost than previous analyzers.
The invention contemplates the utilization of a single beam which alternately irradiates the sample and reference at a relatively slow speed to eliminate costly and complex optics. Obviously, such a system cannot concurrently make both sample and reference measurements. Therefore, it is the purpose of this invention to process these non-concurrent measurements to provide sample and reference values which are effectively unisonous. This is accomplished by synchronously averaging the sample signal about the reference signal or vice versa.
The processing of the signals minimizes or eliminates the effects of drift and improves the signal-to-noise ratio.
Because the error in the signal is minimized electronically, a further advantage is realized, because light detectors having high tolerances, or temperature controls to prevent drift, are no longer required. This will additionally reduce the complexity and cost of the system.